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M. G. Baring (Rice University)
The Einstein source 1E1740.7-2942 near the Galactic Center has been known to exhibit 511 keV line emission that is somewhat variable. suggesting a compact object as its source. Improved observations of hard X-rays about a decade ago saw evidence of a bump at around 170 keV that was not connected to positronium decay emission. This bump was interpreted as part of a Compton reflection feature of the 511 keV line that manifests itself at around 170-511 keV. The reflection is presumed to arise due to the proximity of an accretion disk or some blob of material. The asymmetry of such "target" geometries automatically implies significant hard X-ray/soft gamma-ray polarization that couples to the spectral shape. This paper computes such polarization signatures for certain matter geometries and observational perspectives, thereby providing environmental diagnostics for 1E1740.7-2942 and other accreting compact objects in the galaxy. These model developments are germane to the INTEGRAL hard X-ray/gamma-ray experiment, launched in late 2002, which is expected to measure polarization in this energy band, sensitive to around the 10% level in 1E1740.7-2942 and other galactic and extragalactic sources.
This work was sponsored by the NASA Astrophysics Theory Program.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.